In the technology for supplying pulsed power for the development of high power lasers, flash x-ray machines, nuclear electromagnetic pulse simulators, high energy particle accelerators, and for high powered devices for producing and radiating non-nuclear video pulses, diagnostics has always been difficult. For example, it is sometimes necessary to measure voltages of the order of 10's to 100's of KV at places where the total voltage may rise to levels higher than 15 million volts during a pulse. Not only is it necessary to isolate the voltage monitoring device from ground but it is also necessary to have the voltmeter immuned to damage by suddenly changing inductive fields and RF noise. In the past it has not been possible to make these measurements; however, recently two devices have been disclosed for this purpose. One is an acoustic waveguide voltage monitor, Kenton L. Haynes et al, inventors, U.S. patent application Ser. No. 423,973 filed Sept. 27, 1982 now U.S. Pat. No. 4,514,684. All of the coinventors of the present invention were coinventors of this invention. Haynes et al is a monitoring system which consists of a voltage controlled oscillator for producing acoustic waves whose frequency is proportional to the voltage being measured. An acoustic waveguide is used for transmitting the wave to an electrically isolated acoustic to an electrical transducer. The output of the transducer is amplified and then displayed on an appropriate readout calibrated in watts. However, there are some disadvantages associated with this device in particular environments. The requirement for a power supply at the location where the measurement is to be made not only makes this device larger than desired but it also causes downtime when the prime power source has to be replaced, which is all too often. This also tends to destroy the integrity of the RF shield which leads to the destruction of the device. The integrity of the RF shield degrades with time and use due to vibrations and other motions, thus limiting the life of these devices. In practice this has severly limited the life. The response time of the acoustic device is much too slow to follow rapid changes in the voltage level which may be at GHz rates. The acoustic waveguide is either too stiff to allow easy placement around corners or it is likely to get crimped which stops the transmission of the acoustic wave and causes the device not to operate. And finally the acoustic waveguide has to be unnecessarily long to obtain adequate electrical isolation because of the possible breakdown path in air.
The other device is disclosed in U.S. patent application Ser. No. 454,789, filed Sept. 30, 1982 by Thomas G. Roberts, now abandoned, who is a coinventor of the present invention and relates to a fiber optic guided light wave voltmeter consisting of a diode laser light source, an optical fiber light guide, a polarizer, a polarization analyzer, an optical power meter and a voltage display unit which may be either digital or analog and calibrated in volts. The use of the fiber optic light guide coupled with the application of the photoelastic effects circumvents all the problems associated with the acoustic waveguide voltage monitor. However, it is now necessary to measure the intensity of the light beam which is much more difficult than measuring a frequency. This leads to a rather elaborate calibration procedure with no means other than recalibration to determine that the device has remained in calibration. Also the range of the voltage which may be monitored is limited by the magnitude of photoelastic effect. That is, this device is used in a manner such that the light intensity is 0 at the peak voltage that should be measured. But at higher voltage this effect allows light to pass and the monitor then registers a decrease in voltage instead of an increase in voltage which actually occurred.
The object of this invention is to supply a remotely sensed passive volt meter which does not require a self contained power supply which is completely immuned to RF damage, which is simple and easy to construct at low cost and which is easy to use in that it is passive and does not require calibrating once it has been constructed.